Exhaust noise is a dominant noise associated with an internal combustion engine. Mufflers control and modify the noise produced by exhaust from internal combustion engines. Better acoustic performance of exhaust and other gas mufflers is important for the automobile and other machine-related industries in order to meet community noise standards. Indeed, new regulations are almost continually being proposed which require ever more stringent noise standards.
Some muffler systems use sound attenuating materials like glass fiber. But due to the debris or waste existing in the exhaust gas from internal combustion engines, such absorption materials are seldom used because of the high maintenance cost. Sound absorbing materials also add to the overall cost and weight of the muffler system, restrict the flow of exhaust, and may encourage heat build-up.
An improvement in the noise reduction performance of a muffler is typically accompanied by an undesirable high backpressure. If the muffler is used with an internal combustion engine, a high backpressure results in power loss, engine inefficiency, and high fuel consumption. Numerous muffler designs attempt to attenuate exhaust and other gas noise but little attention paid to the corresponding increase in backpressure. Backpressure is particularly a concern for reactive mufflers that operate on the principle of reflecting acoustic energy back towards the acoustic source.
Although seemingly contradictory, it is desirable to design a muffler that provides substantial noise attenuation without reliance on sound attenuating materials and that also does not generate an accompanying increase in backpressure.